Fiber-optic node with forward data content driven power consumption

ABSTRACT

Methods and systems for modulating an amplifier power supply to efficiently attain amplified RF output power with much lower power dissipation than existing amplifiers. In a cable television (CATV) network, a processor receives a signal to be amplified by an amplifier at a location remote from the processor. A bias point of the amplifier may be variably modulated based on peaks of an input signal to reduce amplifier dissipation.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present disclosure is a continuation of U.S. patent application ser.No. 14/463,011, filed on Aug. 19, 2014, entitled, “FIBER-OPTIC NODE WITHFORWARD DATA CONTENT DRIVEN POER CONSUMPTION”, which claims the benefitof U.S. Provisional App. No. 61/867,550 entitled “Fiber-Optic Node withForward Data Content Driven Power Consumption”, filed Aug. 19, 2013, thecontents of which is incorporated herein by reference in its entirety.

BACKGROUND

A cable television (CATV) system is capable of providing a variety ofmedia content, such as video, data, voice, or high-speed Internetservices to subscribers. The CATV provider typically delivers the mediacontent from a head end to its subscriber's client devices over atransmission network such as a coaxial network, a fiber optic network,or a hybrid fiber/coax (HFC) network. Requirements for data throughput(or bandwidth) in these CATV networks are growing exponentially ascustomers demand more content, data services, etc. Though improvementsin encoding efficiencies and transport protocols have thus far allowedcable operators to keep pace with subscriber and competitive demands, itis important to continue the analysis of the various network elementsthat can enhance or inhibit the overall performance of next-generationcable networks.

Most of the radio frequency (RF) amplifiers within the cable televisionnetwork operate in what is referred to as a “class A” mode of operation,which provides a very high fidelity signal, often quantified in terms ofsignal-to-noise and signal-to-2nd, 3rd, 4th, 5th . . . harmonicdistortion products. However, the power consumption for the class A modeof operation is on the order of 100 times higher than the compositepower of an RF output signal. This higher power consumption results fromthe need to accommodate significant and frequent ‘peak to average’deviations from the effective signal power, which may include settingthe output RF rms amplitude of the amplifier at no more than roughly 25%of the output rail-to-rail range of either voltage or current, dependingon the implementation. The higher demand for power consumption drives upthe cost of cable network products that require RF gain blocs (e.g.,head end optical transmitters and receivers, fiber-optic nodes, RFdistribution amplifiers). Thus, it is desirable to reduce the powerdissipation in a CATV network without compromising output signal powerin relation to noise. It would be even more desirable to reduce thepower dissipation in a CATV network while improving output signal powerin relation to noise.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating embodiments described below, there areshown in the drawings example constructions of the embodiments; however,the embodiments are not limited to the specific methods andinstrumentalities disclosed. In the drawings:

FIG. 1 illustrates an example CATV system.

FIG. 2 illustrates a schematic diagram of a representative basicpush-pull transistor amplifier.

FIG. 3 illustrates the output current that results from an exemplaryinput current to the amplifier shown in FIG. 2

FIG. 4 illustrates the transistor current provided by the amplifier forFIG. 2 in a biased state when providing the amplified signal of FIG. 3.

FIG. 5 illustrates an embodiment of the disclosed digital forwardreceiver.

FIG. 6 illustrates an embodiment for modifying an amplifier biasing.

FIG. 7 illustrates the shape of a signal to amplify.

FIG. 8 illustrates an embodiment of a peak detect algorithm.

FIG. 9 illustrates the input and output waveforms that result from theembodiment shown in FIG. 8.

FIG. 10 illustrates an output signal peak when a bias current is high.

FIG. 11 illustrates exemplary transistor currents.

FIG. 12 illustrates an input signal and output signal scaled toapproximately the same magnitude and compared.

FIG. 13 illustrates an exemplary linearization function.

FIG. 14 illustrates an embodiment with two voltage sources driving atransistor amplifier.

FIG. 15 illustrates a power supply having energy stored in an inductorthat supports power delivery during normal operation and during voltagetransients.

FIG. 16 illustrates an exemplary power supply that delivers a fixedcurrent.

FIG. 17 illustrates an exemplary embodiment that replaces a power supplywith a capacitor.

It should be understood that, while the accompanying figures illustrateembodiments that include the portions of the disclosure claimed, andexplain various principles and advantages of those embodiments, thedetails displayed are not necessary to understand the illustratedembodiments, as the details depicted in the figures would be readilyapparent to those of ordinary skill in the art having the benefit of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure describes systems and methods that reduce powerconsumption in a CATV network, including (1) systems that improve thepower efficiency of a node in a CATV network by drawing power based on asignal; and (2) methods that use signal envelope information to reducepower consumption in a CATV transmission system. As described in moredetail later in this specification, disclosed systems and methodsutilize and expand on many digital forward path concepts, including butnot limited to: 1) analog to digital (A2D) RF signal conversion at oneend of a communication link (e.g., at the head end transmitter side fordigital forward path transmission); 2) oversampling, i.e. sampling at arate larger than the Nyquist frequency of twice the sampled bandwidth soas to enable implementation of sharp digital filtering, which reducesthe number of binary data bits required for RF signal reassembly; 3)compression coding, e.g., Huffman-type encoding, to further reduce thenumber of binary bits required for RF signal reassembly; 4) opticalon/off transmission over required distances, but less than 100 mileswhich is limit specified by the Data Over Cable Service InterfaceSpecification (DOCSIS®) standard; and 5) data decompression at areceiver followed by digital to analog (D2A) signal conversion in orderto reassemble an originally encoded RF signal from a transmitter.

Also, the present disclosure describes systems and methods thatintroduce a delay to be implemented after received data from a signal isdecompressed but prior to the decompressed signal data being amplifiedby a gain block. During the delay, the decompressed data is used topredict the magnitude of the signal envelope that is going to beamplified by the gain block at an incrementally later time. Themagnitude of the signal envelope is then used to generate an auxiliarysignal that drives the power supply to the RF gain block in a mannerthat minimizes the required voltage/current for the gain block, and thusminimizes the power consumed by the block. Moreover, a delayed auxiliarysignal based on the predicted magnitude of the signal envelope incombination with the, optionally delayed, signal itself can be used as afeed-forward pre-distortion signal that corrects for distortionintroduced by the RF gain block when amplifying the signal envelope.

The systems and methods disclosed in the present application can beparticularly useful for reducing the power consumption of a fiberoptical node that has a large number of RF outputs, and acts as the lastamplifier before servicing customer premises—in architecturesalternatively referred to as “fiber to the last active” (FTTLA), Nodeplus zero (N+0), or fiber deep architectures—because in such nodes theRF signals at the output of the node typically consume a relativelylarge amount of power. It should be understood, however, that otherarchitectures or components of other architectures may benefit from thedisclosed techniques, such as upstream or return path A2D/D2A systems,or digital return receivers. Further, the disclosed techniques could beapplied to regulating RF gain stages of other digital forward receivers,even if the receiver is not the last RF gain stage in the downstreamarchitecture. Additional details for various embodiments are describedin more detail below.

FIG. 1 shows an exemplary cable television (CATV) system 100 operable todeliver high-definition digital entertainment and telecommunicationssuch as video, voice, and high-speed Internet services. Generallyspeaking, the CATV system 100 refers to the operational (e.g.,geographical) footprint of an entertainment and/or information servicesfranchise that provides entertainment and/or information services to asubscriber base spanning one or more towns, a region, or a portionthereof. Particular entertainment and/or information services offered bythe franchise (e.g., entertainment channel lineup, data packages, etc.)may differ from system to system. Some large cable companies operateseveral cable communication systems (e.g., in some cases up to hundredsof systems), and are known generally as Multiple System Operators(MSOs).

The cable network can take the form of an all-coax, all-fiber, or hybridfiber/coax (HFC) network, e.g., fiber to the last amplifier (FTTA). Forpurposes of illustration only, FIG. 1 depicts a hybrid fiber-coaxial(HFC) network. An HFC network is a broadband network that combinesoptical fiber and coaxial cable, strategically placing fiber nodes toprovide services to a plurality of homes. It should be understood thatthe systems and methods disclosed in the present application may beemployed in various networks and the HFC network is merely shown as anon-limiting example.

The network shown in FIG. 1 is an HFC broadband network that combinesthe use of optical fiber and coaxial connections. The network includes ahead end 102 that receives analog video signals and digital bit streamsrepresenting different services (e.g., video, voice, and Internet) fromvarious digital information sources. For example, the head end 102 mayreceive content from one or more video on demand (VOD) servers, IPTVbroadcast video servers, Internet video sources, or other suitablesources for providing IP content.

An IP network 108 may include a web server 110 and a data source 112.The web server 110 is a streaming server that uses the IP protocol todeliver video-on-demand, audio-on-demand, and pay-per view streams tothe IP network 108. The IP data source 112 may be connected to aregional area or backbone network (not shown) that transmits IP content.For example, the regional area network can be or include the Internet oran IP-based network, a computer network, a web-based network or othersuitable wired or wireless network or network system.

At the head end 102, the various services are encoded, modulated andup-converted onto RF carriers, combined onto a single electrical signaland inserted into a broadband optical transmitter. A fiber optic networkextends from the cable operator's master/regional head end 102 to aplurality of fiber optic nodes 104. The head end 102 may contain anoptical transmitter or transceiver to provide optical communicationsthrough optical fibers 103. Regional head ends and/or neighborhood hubsites may also exist between the head end and one or more nodes. Thefiber optic portion of the example HFC network 100 extends from the headend 102 to the regional head end/hub and/or to a plurality of nodes 104.The optical transmitter converts the electrical signal to a downstreamoptically modulated signal that is sent to the nodes. In turn, theoptical nodes convert inbound signals to RF energy and return RF signalsto optical signals along a return path. In the specification, thedrawings, and the claims, the terms “forward path” and “downstream” maybe interchangeably used to refer to a path from a head end to a node, anode to a subscriber, or a head end to a subscriber. Conversely, theterms “return path”, “reverse path” and “upstream” may beinterchangeably used to refer to a path from a subscriber to a node, anode to a head end, or a subscriber to a head end. Also, in thespecification, in the drawings, and the claims a node may be any digitalhub between a head end and a customer home that transports localrequests over the CATV network. Forward path optical communications overthe optical fiber may be converted at the nodes to Radio Frequency (RF)communications for transmission over the coaxial cable to thesubscribers. Conversely, return path RF communications from thesubscribers are provided over coaxial cables and are typically convertedat a node to optical signals for transmission over the optical fiber tothe head end. Each node 104 may contain a return path transmitter thatis able to relay communications upstream from a subscriber device 106 tothe head end 102.

Each node 104 serves a service group comprising one or more customerlocations. By way of example, a single node 104 may be connected tothousands of cable modems or other subscriber devices 106. In anexample, a fiber node may serve between one and two thousand or morecustomer locations. In an HFC network, the fiber optic node 104 may beconnected to a plurality of subscriber devices 106 via coaxial cablecascade 111, though those of ordinary skill in the art will appreciatethat the coaxial cascade may comprise a combination of RF amplifiers,taps & splitters and coaxial cable. In some implementations, each node104 may include a broadband optical receiver to convert the downstreamoptically modulated signal received from the head end or a hub to anelectrical signal provided to the subscribers' devices 106 through thecoaxial cascade 111. Signals may pass from the node 104 to thesubscriber devices 106 via the RF cascade 111, which may be comprised ofmultiple amplifiers and active or passive devices including cabling,taps, splitters, and in-line equalizers. It should be understood thatthe amplifiers in the RF cascade 111 may be bidirectional, and may becascaded such that an amplifier may not only feed an amplifier furtheralong in the cascade but may also feed a large number of subscribers.The tap is the customer's drop interface to the coaxial system. Taps aredesigned in various values to allow amplitude consistency along thedistribution system.

The subscriber devices 106 may reside at a customer location, such as ahome of a cable subscriber, and are connected to the cable modemtermination system (CMTS) 120 or comparable component located in a headend. A client device 106 may be a modem, e.g., cable modem, MTA (mediaterminal adaptor), set top box, terminal device, television equippedwith set top box, Data Over Cable Service Interface Specification(DOCSIS) terminal device, customer premises equipment (CPE), router, orsimilar electronic client, end, or terminal devices of subscribers. Forexample, cable modems and IP set top boxes may support data connectionto the Internet and other computer networks via the cable network, andthe cable network provides bi-directional communication systems in whichdata can be sent downstream from the head end to a subscriber andupstream from a subscriber to the head end.

The techniques disclosed herein may be applied to systems compliant withDOCSIS. The cable industry developed the international Data Over CableSystem Interface Specification (DOCSIS®) standard or protocol to enablethe delivery of IP data packets over cable systems. In general, DOCSISdefines the communications and operations support interface requirementsfor a data over cable system. For example, DOCIS defines the interfacerequirements for cable modems involved in high-speed data distributionover cable television system networks. However, it should be understoodthat the techniques disclosed herein may apply to any system for digitalservices transmission, such as digital video or Ethernet PON over Coax(EPoc). Examples herein referring to DOCSIS are illustrative andrepresentative of the application of the techniques to a broad range ofservices carried over coax.

References are made in the present disclosure to a Cable ModemTermination System (CMTS) in the head end 102. In general, the CMTS is acomponent located at the head end or hub site of the network thatexchanges signals between the head end and client devices within thecable network infrastructure. In an example DOCSIS arrangement, forexample, the CMTS and the cable modem may be the endpoints of the DOCSISprotocol, with the hybrid fiber coax (HFC) cable plant transmittinginformation between these endpoints. It will be appreciated thatarchitecture 100 includes one CMTS for illustrative purposes only, as itis in fact customary that multiple CMTSs and their Cable Modems aremanaged through the management network.

The CMTS 120 hosts downstream and upstream ports and contains numerousreceivers, each receiver handling communications between hundreds of enduser network elements connected to the broadband network. For example,each CMTS 120 may be connected to several modems of many subscribers,e.g., a single CMTS may be connected to hundreds of modems that varywidely in communication characteristics. In many instances severalnodes, such as fiber optic nodes 104, may serve a particular area of atown or city. DOCSIS enables IP packets to pass between devices oneither side of the link between the CMTS and the cable modem.

It should be understood that the CMTS is a non-limiting example of acomponent in the cable network that may be used to exchange signalsbetween the head end and subscriber devices 106 within the cable networkinfrastructure. For example, other non-limiting examples include aModular CMTS (M-CMTS™) architecture or a Converged Cable Access Platform(CCAP).

An EdgeQAM (EQAM) 122 or EQAM modulator may be in the head end or hubdevice for receiving packets of digital content, such as video or data,re-packetizing the digital content into an MPEG transport stream, anddigitally modulating the digital transport stream onto a downstream RFcarrier using Quadrature Amplitude Modulation (QAM). EdgeQAMs may beused for both digital broadcast, and DOCSIS downstream transmission. InCMTS or M-CMTS implementations, data and video QAMs may be implementedon separately managed and controlled platforms. In CCAP implementations,the CMTS and edge QAM functionality may be combined in one hardwaresolution, thereby combining data and video delivery.

Orthogonal frequency-division multiplexing (OFDM) may utilize smallersub-bands (compared to QAM carriers). For example, while a conventionalDOCSIS QAM carrier is 6 MHz wide, the CATV system may employ orthogonalfrequency division multiplexing (OFDM) technology with OFDM carriersthat are approximately 25 kHz to 50 kHz wide. Thus, where previously 100QAM carriers were used, thousands of OFDM subcarriers may be used. OFDMtechnology may be suitable for noisy signal conditions and may enableuse of more of the available spectrum without reducing the quality ofserver. In example implementations, a cable network may use the QAMmodulation for downstream speeds and boost upstream speeds using OFDM.

FIG. 2 shows a representative schematic of a basic push-pull transistoramplifier 200 that amplifies an input signal 210 driven by adifferential voltage from supply V2 to produce an output signal 220through resistor R14. The amplifier 100 draws current supplied to twotransistors Q1 and Q2 to provide the desired amplified signal voltageacross the resistor R12. Resistors R11 and R12 set an input impedance tothe amplifier of around 200 Ohms. Power supply V4 provides a commonvoltage to the inputs that is used to set a current bias point of theamplifier. Each transistor has a feedback resistor R2 and R4,respectively to the collectors of the transistors, which are connectedto the low impedance differential load R10 that is provided the outputvoltage signal 220 across it. Transformer 230 connected to voltagesource V1 is also used to bias the amplifier by providing a highimpedance to differential signals and a low impedance to common modecurrent.

FIG. 3 shows the input current 250 through resistor R11 and the outputcurrent 260 through the resistor R14 of the amplifier circuit 200, for amulti-channel modulated RF signal typical for CATV nodes. The currentgain is large (>20×). The output amplitude is usually close to anaverage rms value but occasionally high amplified signal peaks occur.The peak values are typically on the order of 6 times the rms value witha relatively low probability (in time) on the order of 10^−6. However,since amplifier clipping leads to bit errors in RF communication links,the amplifiers must amplify these peaks with high fidelity even thoughthe occurrence rate is relatively low.

In order to provide the required current gain to amplify a signal withthe large signal peaks shown in FIG. 3, the amplifier must usually bebiased at a high current. Thus can be most easily seen in FIG. 4, whichshows the amplifier current used by the transistor Q2 in the amplifier200 of FIG. 2 where the amplifier is biased at approximately 80 mA. Whenamplifying the signal 250 shown in FIG. 3, during the peak in outputvoltage the current in the transistor Q2 falls to just under 10 mA. At 0mA the amplifier would have been unable to further amplify the signaland clipping distortion would have occurred. Stated differently, werethe amplifier circuit 200 not biased to 80 mA but biased at a lowerpoint, or alternatively, if the input to the amplifier had a highersignal peak to be amplified, clipping would have occurred along with theattendant signal degradation (bit error) that accompanies distortionfrom amplifier clipping.

RF amplifiers in an HFC network typically operate in a “Class A” mode ofoperation, meaning that they provide a high fidelity amplified signalwhere the bit error rate should be no more than approximately 10⁻⁸. Asjust noted, given that the signal peaks occur at a rate of 10⁻⁶, i.e.100 times the frequency of the required bit error rate, the RFamplifiers in an HFC network must provide a sufficiently high bias pointthat only approximately one in a hundred or less of the amplified signalpeaks are clipped. Because the signal peaks occur so infrequently,however, and because the signal peaks are approximately six times higherthan the rms value of the signal, biasing the amplifier to account forthe signal peaks makes the amplifier circuit highly inefficient. In atypical case, for example, to provide 100 mW of total RF output of theamplified signal, about 10W of power is required, i.e. only about 1% ofthe power supply to the amplifier is used to provide the RF energyoutput while the remainder of the power is consumed to bias theamplifier at a current that is almost always much higher than necessaryto amplify the signal, except for the infrequent signal peaks.

There are more than four million amplifiers dispersed throughout HFCnetworks in the United States alone. This translates into a total energyconsumption in the millions of dollars per year, which as just noted ismostly energy that is only needed to amplify highly sporadic signalpeaks.

FIG. 5 shows an exemplary receiver 300 capable of being used in a node104 to modulate an amplifier power supply so as to efficiently attainamplified RF output power with much lower power dissipation thanexisting amplifiers. The receiver 300 may preferably include adecompression module 310 that receives radio frequency data anddecompresses it, but could also include other means to generate adigital waveform. Prior to amplifying the decompressed data, thereceiver 300 introduces a delay 320 before processing the signal by anoptional pre-distortion module 330 and inputting the signal to a D2Aconverter 340 that drives the input signal to an amplifier 350 having again block 360 and power supply 370.

During the delay 320, the receiver 300 preferably includes an analysismodule 380 that analyzes the decompressed radio frequency data, i.e. thesame data that comprises the input signal to the amplifier 350, and usesthe data to create a modulation signal to the power supply 370 throughD2A converter 390. The modulation signal can comprise any one of anumber of alternate forms. For example, in a simple embodiment, thepower supply 370 may be modulated in a binary manner between a normal(low) bias point used during the periods when the signal is notexperiencing signal peaks and a peak (high) bias point when the signalis experiencing signal peaks. Because of the delay 320, the bias pointof the amplifier 350 may be modulated in a synchronous manner with thesignal that it amplifies so that the bias point is raised as the signalexperiences a peak and is lowered as the signal falls from the peak. Inother embodiments, more complicated modulation schemes may be employed,such as switching the bias between more than two bias points to accountfor variances in the amplitudes among signal peaks, or even modulatingthe bias voltage or current of the amplifier in a manner that is linearwith respect to the signal amplitude at any point in time. It should beunderstood that the delay 320 may be introduced at any time beforeamplifying the data so that the amplified data coincides with themodulation signal, and that the illustration of the delay occurringafter decompression is illustrative only, particularly given that somesystems may not include compressed data, or otherwise need to decompressdata for amplification.

The receiver 300 may also optionally include many of the components thatmake up a digital return transmitter, with the addition of an A2Dconverter. The digital forward receiver can thereby perform the functionof a digital return transmitter with bandwidths of 85, 2×85, 200 or2×200 MHz using a bidirectional optical pluggable in the 4.25 Gbs or11.3 Gbs port. Thus, the digital forward receiver can be converted toessentially most of the components of a node with forward and reversetraffic for a small added cost.

As can be appreciated by those of ordinary skill in the art, thereceiver 300 can use signal processing to predict power envelopes andautomatically compensate amplifier artifacts due to supply modulation bygenerating a compensation signal in the output D2A converter. The biaspoint of the amplifier (current and/or voltage) may be modulated toreduce amplifier dissipation. In some embodiments, the receiver 300 candissipate on the order of 4 times less supply power for a given outputpower level. Less power used by the receiver 300 enables the use ofsmaller transistors, a smaller heat-sink, lower cost packaging, and areduction of the node size and power consumption.

It should be noted that while embodiments disclosed herein describe anode amplifier solution for power reduction, the concepts apply forother amplifiers in the cable network. For example, embodiments mayincorporate modulation of analog amplifiers cascaded in the field thatmay not be driven directly by D/A converters. In an amplifier in thecascade of amplifiers, lower cost amplifiers are desirable. Asdisclosed, embodiments for the cascaded amplifier may provide a lowercost amplifier via the reduction of the power dissipation with a higheroutput power capability as an option. Where the cable network has beenupgraded, lower cost amplifiers that reduce power dissipation but allowhigher output are desirable.

Embodiments disclosed for creating a more efficient amplifier arebeneficial for existing networks and advanced or next generationnetworks. For example, even if an advanced architecture, e.g., theNode+0 architecture is not adopted, amplifiers that are more powerefficient are still desirable. Given that amplifiers compensate for thelosses in the leg preceding them, a universal setting from the nodeworks on a collection of amplifiers. As most amplifiers have a similartilt and gain setting and are operated with a similar power load, by andlarge the same setting will apply to a chain of amplifiers.Architectures will have shorter and shorter amplifier chains to settleon advanced architectures, e.g., N+1 or N+2.

The disclosed digital forward architecture permits very low cost andpower efficient nodes. For example, embodiments for the discloseddigital forward techniques allow small cost and power efficient nodedesigns that enable node replacement and also fiber deep architecturesthat are currently inhibited by node cost and by maximum wavelengthcounts on fiber. Furthermore, in embodiments where all processing is inthe digital domain, there is flexibility in the band-split of such adesign. Almost any RF gain stage can benefit from the disclosedtechniques where a digitized input signal is made, delayed, and used asa decision input for a power supply and predistortion input. Existingstandard HFC gain stages do not have a benefit of the digitized signal,thus the disclosed digital forward (and digital return) systemsdisclosed may benefit from the disclosed techniques for the receivingside of the system and the corresponding output RF gain stage (with acost effective, minimal functional blocks/cost addition).

It should be noted that various implementations for the disclosedtechniques are possible wherein the supply voltage and/or the transistorbias are modulated. The push and pull transistors may be independentlydriven by D2A converters to permit true class B operation or class Boperation combined with supply modulation. Such manipulations can causedistortions in analog the output signal; however the distortions arepredictable. The digital pre-distorter 330 in the receiver 300 mayoptionally be used to mitigate the distortions.

7)

FIG. 6 depicts an exemplary push-pull amplifier 400 having a powersupply 410 capable of being modulated using the receiver 300 such thatthe bias current is high only when a high peak needs to be amplified andlow otherwise by adding a voltage source V3. The voltage source V3 isdriven by a signal that is generated such that the bias is high whenoutput peaks need to be amplified. FIG. 7 shows a waveform 420representing the voltage provided from the voltage source V3 and awaveform 430 representing the shape of the signal to amplify. The biassignal is seen to increase when an output peak needs to be amplified. Inthe embodiment depicted in FIGS. 6 and 7, the bias signal was digitallygenerated by passing samples of the signal to amplify through a peakdetection circuit and a subsequent filter, while the main signal (thesolid line shown in FIG. 7) was delayed by a number of samples such thatthe response of the bias signal would coincide with the signal peak.

FIG. 8 illustrates an embodiment in which an analysis module 450 maydetect both positive and negative peaks, and may calculate the absolutevalue of the RF signal to amplify before performing a peak detection orpower detection operation. The amount of delay 460 is set such that thebias signal, after filtering by filter 470, can reach a peak valueconcurrently with a peak in the RF input signal to amplify. The RFsignal can be output to a D2A converter to create an analog signal. Thecontrol bias signal can also be output to a D2A converter to create ananalog bias signal.

Resulting input waveform 480 and output waveform 490 from the embodimentof FIG. 8 are each shown in FIG. 9, which can be easily seen as areproduction of the input and output waveforms of Fig, 3. FIG. 9 showsthat the receiver's amplification of the input signal is unchanged.However, as can be seen in FIG. 10, the current from the power source V1is no longer a constant current. The modulation of the bias point of thetransistors results in a modulation of the power supply current from thetransformer 415 of FIG. 6. FIG. 10 illustrates that when the outputsignal peak occurs the bias is actually high, peaking as high as 200 mAin this example. On average the bias current is much lower than in theprevious example; 82 mA in this case. The power consumption of theamplifier has been reduced by a factor of approximately two (as seen incomparison to waveform 430 of FIG. 7). The transistor currents are shownin FIG. 11; as with the comparison for FIG. 11 and FIG. 7, thecomparison of FIG. 11 to FIG. 10 also shows an approximate reduction inpower by a factor of two, where the lowest value is again just under 10mA, but this is accomplished by a bias current of only approximately 40mA per transistor instead of the original 80 mA.

Because the power supply via transformer 415 of FIG. 6 is insensitive tocommon mode current fluctuations (these are passed with littleresistance) and because the differential output signal in R14 is alsonot sensitive to common mode fluctuations, the push-pull amplifier shownin FIG. 6 is particularly suitable for modulation of the bias currentwithout affecting the signal to amplify because the bias control signalis self-cancelled in the output resistor R14. FIG. 12 illustrates aninput signal 500 and output signal 510 that are scaled to approximatelythe same magnitude and compared; the input signal is amplified andreproduced with high fidelity.

In CATV systems, however, extreme requirements can be applied to thefidelity of signal amplification. It is known that there is somedependence of the distortion behavior of amplifiers on the bias point.Accordingly, FIG. 13 shows an analysis module 550 that includes alinearizer 560 that applies a linearization function in the delayedsignal path to drive the amplifier, where the parameters of thelinearizer can optionally be controlled by the bias point of theamplifier. The implementation of the linearizer can be similar tolinearizers used in laser optic transmitters (e.g., linearizerimplementations that include digital signal implementations in FPGAs anddiscrete component implementations in RF components) such as U.S. Pat.Nos. 8,064,777, 8,547,174 and 8,145,066 as well as U.S. PatentApplication Pub. No. 20030001670. The embodiment shown in FIG. 13 issuitable for systems where the signal is digitally processed such thatall operations are in the digital domain. However, it should beunderstood that an implementation in the analog domain with RFcomponents is also possible, including peak detection, delay, biassignal generation and/or linearization functionalities.

It should also be understood that in some embodiments, the bias controlsignal and the RF signal to amplify need not be generated separately onD2A converters. For example, FIG. 14 depicts a push-pull amplifier 600having two voltage sources 610 and 620 driving the differentialtransistor amplifier, each voltage source providing both bias controland RF signal information to the transistors. The overall signalamplified by the transistors can be the same as in the example depictedin FIGS. 9-11. Moreover, while the amplifier bias current can becontrolled and modulated to reduce power dissipation, the amplifier biasvoltage can also be controlled and modulated to reduce power dissipationor a combination thereof.

In some embodiments where the power supply is modulated, the combinationof bias current and voltage supply modulation can yield further powersavings, for instance by a factor of four instead of a factor of two aswas shown with bias modulation only. However, the construction of amodulated voltage supply is more complex than modulating the biascurrent of the transistors. FIGS. 15-17 show embodiments for a powersupply with energy stored in an inductor that supports power deliveryduring normal operation and during voltage transients FIG. 15, forexample, shows a power supply 700 with the main power supply 710 set to11V, for example. The power supply 700 may provide current throughinductor 715 with a parasitic internal resistance R1 (e.g., a 10 mOhm to1 Ohm resistor, 900 mOhm in this example). A variable voltage source 720comprising a series connection of first fixed voltage source 725 and asecond variable voltage source 730 is shown connected in parallel withthe load 735. The variable voltage of the voltage supply 730 is made tobe proportional to a bias control signal.

As shown in FIG. 16, in a bias voltage control transient, the voltageacross load R2 peaks from around 10V to around 22 V, as seen in curve750. The current from power supply 710, seen as curve 745, is fixed atabout −1A. The current from power supply 720, seen in curve 740 peaks toabout −1.2A during the transient, but otherwise it is small (−0.1 A orless). Except for the transient, nearly all the power is delivered bypower source 710. Power source 720 has enough headroom to provide twicethe supply voltage but only delivers power during the transient andwhile it is delivering power the power source 710 continues to deliverpower due to the inductance of the inductor 715 that holds the currentconstant during the transient. As a result the average power deliveredby power source 710 (1A) is much larger than the average current fromsource 720 (0.12 A). Since power source 725 needs to be able to reach22V it is generally implemented with a 22 V source and a transistorstage following that to create the transient waveform. Thus we canestimate power dissipation in the voltage source 710 can be estimated at11 W (11V×1A) and the power dissipation in voltage source 720 estimatedat 2.64 W (22V×0.12A). The total, 13.64 W is much lower than the 25.64 W(22V×1.12A) that would be the case if a fixed 22V power supply was usedfor the full current.

As shown in FIG. 17, some embodiments may replace the voltage supply 725by a capacitor 760. In this example, the capacitor 760 may self-chargeto around 10V so that an external 22V supply is no longer needed. Thecapacitor 760 is large enough to retain the 10V difference during thesurge and the voltage supply 720 can be driven from a 12 V supply; noother higher voltage supply is needed.

In some embodiments, the presence of inductor 715 is essential to keepthe current through the transient voltage generator 730 low as theinductor 715 supports the average current during normal operation wherethe output voltage is close to the main power supply, the main powersupply provides all the power, and the inductor 715 sustains thatcurrent during transients where the voltage could be much higher (forinstance doubled) so that the transient voltage generator only needs togenerate the additional current needed excluding the average currentthat was already provided by L1. Enhanced amplifier operation.

In one or more examples, the functions disclosed herein may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted as one or more instructions or code on a computer-readablemedium and executed by a hardware-based processing unit.Computer-readable media may include computer-readable storage media,which corresponds to a tangible medium such as data storage media, orcommunication media including any medium that facilitates transfer of acomputer program from one place to another, e.g., according to acommunication protocol. In this manner, computer-readable mediagenerally may correspond to (1) tangible computer-readable storage mediawhich is non-transitory or (2) a communication medium such as a signalor carrier wave. Data storage media may be any available media that canbe accessed by one or more computers or one or more processors toretrieve instructions, code and/or data structures for implementation ofthe techniques described in this disclosure. A computer program productmay include a computer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. “Disk” and“disc” as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses. Various components, modules, or units aredescribed in this disclosure to emphasize functional aspects ofcomponents configured to perform the disclosed techniques, but do notnecessarily require realization by different hardware units. Rather, asdescribed above, various units may be combined in a codec hardware unitor provided by a collection of interoperative hardware units, includingone or more processors as described above, in conjunction with suitablesoftware and/or firmware.

The invention claimed is:
 1. A device having an amplifier operable foramplifying an input signal, the device reducing power dissipation bymodulating an amplifier power supply, the device comprising: a firstamplifier power supply, wherein an amplifier amplifies signals withpower provided via an output from the first amplifier power supply; anda second amplifier power supply driven by a bias signal generated bypassing samples of the input signal to amplify through a peak detectioncircuit, a second amplifier power supply output causing variable changesto a bias point of the amplifier to coincide with peaks in the inputsignal, wherein the bias point of the amplifier modified by the secondamplifier power supply output is varied to reduce power consumption ofthe amplifier; a linearizer that receives a delayed input signal and anenvelope signal of the bias signal and applies a linearization functionto the delayed input signal for driving the amplifier by the delayedinput signal adjusted in response to changes in the envelope signal ofthe bias signal, wherein the delayed input signal is the input signaldelayed by a number of samples for coinciding a response of the biassignal with at least one peak in the input signal; and an outputtransformer of said amplifier with coupled windings for reducingresistance to common mode current fluctuations caused by the changes tothe amplifier bias point.
 2. The device of claim 1, where amplificationof the input signal comprises amplification of a first component of theinput signal, and prior to such amplification another component of theinput signal pre-distorts the first component prior to amplification. 3.The device of claim 2, wherein the another component is based on thefirst component and a signal envelope of the first component.
 4. Thedevice of claim 1, wherein the first component and the another componenthave an associated delay between them.
 5. The device of claim 1, whereinpre-distortion information is transmitted to the amplifier with saidinput signal, the pre-distortion information based on said input signaland an envelope of said input signal.
 6. The device of claim 1, whereinthe second amplifier power supply provides bias to the amplifier via aninductor connected to a fixed voltage.
 7. The device of claim 1, furthercomprising a capacitor connected to the second amplifier power supply togenerate a variable voltage, wherein the variable voltage is controlledby a signal derived from the envelope of a signal output from theamplifier.